An Auger investigation of the grain-boundary chemistry in Ni3(Si,Ti) alloys

Three different Ni3(Si,Ti) alloys were cathodically charged with hydrogen and fractured under high vacuum conditions. Scanning Auger microscopy (SAM) and scanning electron microscopy (SEM) were used to determine the chemical compositions of the fracture surfaces and the mode of fracture. The compositions of the transgranular regions were compared with the intergranular regions in order to determine the amount of grain-boundary segregation or depletion of the various constituents. In all the alloys studied, Si and Ti were depleted on the grain boundaries, while Ni was enriched relative to the bulk. Correlations were made between the grain-boundary compositions and the previously reported environmental embrittlement of these alloys. An embrittlement factor defined as [(Si+Ti)/Ti] on the grain boundaries is suggested to be related to the degree of environmental embrittlement at ambient temperatures. Some possible reasons for this correlation are discussed.